A power train, i.e. an engine-transmission assembly, for a motor vehicle is typically mounted to a power train frame structure that is in turn mounted to the motor vehicle frame. To function properly, power train mounting systems are configured to support the power train and to insulate the vehicle frame from power train noise and vibrations generated by the power train. Three-point and four-point principal axis of inertia mounting systems are well known in the art; these mounting systems support the power train at three or four locations and are positioned over the principal axis of inertia, which intersects the power train's center of gravity.
In conventional four-point mounting systems, an engine mount and a transmission mount support most of the load of the power train. The engine and transmission mounts, which serve as the two main mounts, are placed over the power train's principle axis of inertia to improve Noise, Vibration, and Harshness (NVH) levels. The front and rear portions of the power train are further supported by roll mounts, providing two additional support points, to control the vehicle's roll displacement. See U.S. Pat. No. 6,708,793, which is incorporated herein by reference in its entirety.
However, conventional principal axis of inertia four-point mounting systems are inadequate for supporting high performance and/or high power engines, e.g. V-6 engines, etc. These engines tend to be heavier and to generate a large torque; large vehicle roll displacement therefore results with increased inertia and engine output. A way to restrict the amount of roll displacement is to dramatically raise the spring constant of the roll mount. However, too high a spring constant will result in poor NVH performance when the vehicle is idling since the roll mounts will not be as effective in damping torque-related vibrations from the power train. Moreover, the spring constant of the roll mount is typically low in conventional principal axis of inertia four-point mounting systems. As a result, roll displacement becomes more and more amplified by action-reaction forces from the power train and roll mounts, respectively, with increasing engine output, and the roll mounts become compressed to the point where power train noise and vibrations can be readily felt by passengers during a vehicle start.